Performance of solar dryer chamber used for convective drying of sponge-cotton

Abstract

Solar dryer chamber is designed and operated for five days of July 2008. Drying experiments are conducted for sponge-cotton; as a reference drying material in the ranges between 35.0 to 49.5?C of ambient air temperature, 35.2 to 69.8 ?C drying air temperature, 30 to 1258 W/m2 solar radiation and 0.016 to 0.08 kg/s drying air flow rate. For each experiment, the mass flow rate of the air remained constant throughout the day. The variation of moisture ratio, drying rate, overall dryer efficiency, and temperature distribution along the dryer chamber for various drying air temperatures and air flow rates are discussed. The results indicated that drying air temperature is the main factor in controlling the drying process and that air mass flow rate has remarkable influence on overall drying performance. For the period of operation, the dryer attained an average temperature of 53.68?C with a standard deviation of 8.49?C within a 12-h period from 7:00 h to 19:00 h. The results of this study indicated that the present drying system has overall efficiency between 1.85 and 18.6 % during drying experiments. Empirical correlations of temperature lapse and moisture ratio in the dryer chamber are found to satisfactorily describe the drying curves of sponge-cotton material which may form the basis for the development of solar dryer design charts.